Full-surround spherical screen projection system and recording apparatus therefor

ABSTRACT

A projector  3  is provided for casting light toward the inside of a spherical screen  2 . A first reflecting mirror  4  is arranged inside the spherical screen  2  on the optical axis  15  of the projector  3 , and a second reflecting mirror  5  of a convex mirror on the optical axis  15  is arranged adjacent to a body tube  16  of the projector  3 . The light emitted from the projector  3  is cast onto the entire surface of the spherical screen  2  via the first and second reflecting mirrors  4, 5 . Images with virtual presence can be projected onto the entire surface of the spherical screen by the simple structures using the single projector.

TECHNICAL FIELD

The invention relates to a full-surround spherical screen projectionsystem that projects recorded images or computer graphic images, andparticularly to a full-surround spherical screen projection system thatcan be used to project scenery of cities, housing spaces, flightsimulators, game apparatuses and planetariums.

BACKGROUND ART

Recently, as a virtual reality visual display system that can givepresence—the same feeling as if placed in a real situation—an immersiveprojection display which encloses viewers with a large screen projectedin from the back has drawn attention. A sphere is an ideal shape for animmersive screen in that a distance from the viewer's eye to theprojected images remains constant.

As a solid angle subtended by an image with respect to a viewer becomeslarger, it is impossible to project the image sufficiently. Therefore,conventionally, from a plurality of plane screens was formed apolyhedral screen, on which the images recorded by a plurality of wideangle cameras corresponding to the plane screens were thrown byprojectors.

However, when a plurality of cameras arc used, there is a dead anglebetween adjacent cameras that does not allow recording. The dead anglemay be negligible with respect to a subject in the distance, but as fora subject close by, the image of the subject corresponding to thedistance between the edges of the lenses of adjacent cameras is missing.

The structure in a combination of plane screens produces a problem inthat the ridges in the seams of each screen give an unnaturalimpression. In CG (Computer Graphic) images, a geometric correction ismade to cope with the problem. Making a correction of recorded images,especially motion images, is difficult in original formatting stages. Todo this, a plurality of cameras arc needed and it takes time to correctthe original images, which increases cost.

To solve, in principle, the problems of the dead angle and seams, it isnecessary to obtain the images of a large solid angle by a single-systemcamera and project them onto a spherical screen by a single-systemprojector. Conventionally, as a means of a single-system projectorthrowing images on a spherical screen, fisheye lenses were used to throwimage onto a semi-spherical screen. Yet, since the means produces ashadow when a viewer enters a semi-sphere projection screen, a viewermust view the screen from the outside of the semi-sphere, indicatingthat, in principle, enclosing a viewer at a solid angle of more than 2πis impossible. As a result, the means is not suitable to an immersiveprojection display.

In addition, a means can be thought of that, by a computer, controls,moves and tilts a reflecting mirror for the light from one projector toproject in a wide range of angles onto a spherical screen. Yet thatsystem cannot project entirely onto a spherical surface, and thestructure is complex and expensive.

It is an object of the invention to solve the problems in the prior art.There is provided a full-surround spherical screen projection systemthat forms a spherical screen inside of a sphere, places a single-eyedprojector, over a viewer, for projecting images in the inner directionof the sphere, provides, inside of the spherical screen, a firstreflecting mirror opposed to the projector, provides a second reflectingmirror adjacent to the projector, and projects the images through thefirst and second reflecting mirrors from the projector on the screen.The screen projection system can throw images on the entire surface ofthe spherical screen except for the top and bottom of the sphere, with awide visual field angle to the upper and lower directions and withoutcasting a shadow by the viewer. The screen projection system is simplein structure, low in cost and spacious for the viewer.

The full-surround spherical screen projection system can be used tothrow recorded images and CG images. At the stage of making originalimages to be thrown, distortion may be added to the original imagesbeforehand. When thrown onto the spherical screen, the distortion of theimages will be cancelled out to produce images without distortion.

DISCLOSURE OF INVENTION

To solve the problems, the invention provides a full-surround sphericalscreen projection system comprising a spherical screen formed inside ofa sphere, a projector for projecting light toward the inside of thesphere, a first reflecting mirror constituting either a plane mirror ora concave mirror, placed above the center of the sphere inside of thesphere, for reflecting the light toward the outside of the sphere, and asecond reflecting mirror constituting a convex mirror reflecting thelight from the first reflecting mirror to the spherical screen, wherebythe light from the projector is thrown on the entire surface of thespherical screen through the first and second reflecting mirrors.

The sphere may have an opening at a portion thereof, and the secondreflecting mirror is placed in opposed to the opening within a radiusfrom the center of the sphere.

The projector and the first and second reflecting mirrors are placed onthe same optical axis, and the second reflecting mirror is either acircular reflecting mirror with a central hole that passes the lightthrough from the projector or a half mirror.

The projector and the second reflecting mirror may be placed apart tothe side along the inner wall of the sphere.

The projection system is used to throw images recorded by a projector orcomputer-generated images. The recorded images are made by a recordercomprising an elliptical convex mirror according to a curvature of thesecond reflecting mirror, a subject being recorded through theelliptical convex mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a full-surround spherical screenprojection system in accordance with the present invention.

FIG. 2 is a sectional view with respect to A—A in FIG. 1.

FIG. 3 shows the relationship between a projected image and a screenimage in accordance with the present invention.

FIG. 4 is a plane view of an embodiment of an image recording apparatus(recorder) in accordance with the present invention.

FIG. 5 shows a second embodiment of a full-surround spherical screenprojection system in accordance with the present invention.

FIG. 6 shows a third embodiment of a full-surround spherical screenprojection system in accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be explained in more detail, referring to the figuresshowing the embodiments of the inventions. FIGS. 1 and 2 show a firstembodiment of a full-surround spherical screen projection system inaccordance with the present invention. FIG. 1 is a sectional view of afull-surround spherical screen projection system 1 seen from one side.FIG. 2 is a sectional view with regard to A—A in FIG. 1. In FIGS. 1 and2, the full-surround spherical screen projection system 1 includes aspherical screen 2, a projector 3, a first reflecting mirror 4 and asecond reflecting mirror 5, and is placed in a room 6, for example.

Openings 8, 9 are formed on a top and a bottom of a sphere 7,respectively. On the inside of the sphere 7, a screen surface 11 isprovided to form the spherical screen 2. The material constituting thesphere 7 of the spherical screen 2 must be that which can maintain thestructure of spherical shell of the sphere 7, such as plastic, metal,etc. To reduce reflecting sound in the sphere, it is preferable that itbe a sound-absorbing material.

Conventional materials can be used for the screen surface 11. Thespherical screen 2 is suspended from a ceiling wall 12 of a room 6 by adangling support 18. The spherical screen 2 can be placed on legs thatare fixed on a floor 10, or attached to a side wall of the room 6.

The projector 3 is placed on a central axis 14 of the sphere 7corresponding to the surface 8. A light axis 15 of the projector 3 ispresent on the central axis 14 of the sphere 7.

The projector 3 may be any type of a liquid projector, a CRT projectoror a film projector. Projected images may be any image of recordedimages obtained by recording, or images generated by a computer. In theembodiments, projectors are attached to the ceiling wall 12 of the roomand projected toward the inside of the sphere 7 through a body tube 16.

The first reflecting mirror 4 is positioned above the center of thesphere inside of the spherical screen, opposed to the mouth of the bodytube 16 of the projector, the center of the mirror being on a light axis15 of the projector 3. The first reflecting mirror 4 is suspended andsupported from the ceiling wall by, for example, an attachment bar (notshown) such as a gut.

The positioning of the first reflecting mirror 4 is related to aprojecting distance of the projector. As shown in FIG. 1, when thesphere 7 is small compared with a viewer and the projecting distance ofthe projector, the first reflecting mirror 4 is positioned slightlyabove the center of the sphere. However, when the sphere 7 is largecompared with the projecting distance of the projector, the firstreflecting mirror 4 is positioned higher above the center of the sphere.

On the other hand, because the center of the sphere is the mostappropriate position for viewing, it is preferable that a viewer viewsfrom the center. In the invention, because the first reflecting mirroris placed above the center of the sphere, enough space is made at thecenter so that the viewer can view from the center without interferenceby the first reflecting mirror. For example, even when viewing from thecenter of the sphere, the viewer need not bend to avoid the projectionoptical system including the optical elements of the projector overhead,the first reflecting mirror and the second reflecting mirror, especiallythe first reflecting mirror, nor care about the system, which increasesflexibility and enhances good viewing.

The first reflecting mirror 4 is formed by a plane mirror or a concavemirror. When the first reflecting mirror is a plane mirror, a dip, whichreaches to the lower portion of the projected light reflected by thesecond reflecting mirror, is increased more than in a concave mirror. Asa result, the upper and the lower visual fields are increased more thanin a concave mirror. However, when the first reflecting mirror is aconcave mirror, the space between the first reflecting mirror and theprojector can be made smaller, which makes the projection optical systemcompact.

The second reflecting mirror 5, opposed to the opening 8 and the bodytube 16 of the projector 3, is placed on the optical axis of theprojector 3, with the distance from center O of the sphere 7 to thesecond reflecting mirror 5 shorter than a radius R of the sphere 7. Thesecond reflecting mirror 5 has a central hole 17 which allows theprojected light to pass through, and is formed in a ring shape (adoughnut shape). The center of the second reflecting mirror 5, which isattached to the ceiling wall 12 through an attachment bar (not shown)such as a gut, lies on the light axis 15. The mirror surface of thesecond reflecting mirror 5 is shaped to be a convex mirror and ismanufactured, for example, by precisely grinding aluminum alloy andperforming surface processing such as plating and electrolyte polishing.The second reflecting mirror 5 can be a half mirror, rather than acircular mirror with the central hole 17.

In the projection optical system of the above first embodiment, whichincludes the projector, the first and second reflecting mirrors, eachoptical element is placed on the same optical axis. The scope of thespherical screen is axially symmetrical. However, in the optical systemof the invention, each optical element is not necessarily placed on thesame optical axis. When the image scope of the spherical screen 2 is notsymmetrical with a large bias in the forward direction and a small biasin the backward, the projector can be arranged so that it can beprojected at a slant.

As a modification of the first embodiment, the projector may be placedto the side (the circumferential direction of the sphere 7), with theoptical axis of the projector shifted from that of the second reflectingmirror. With respect to the first reflecting mirror, for example, theprojected light is hit at an angle from the back and above. As a result,a full-surround spherical screen projection system can be realized thatprojects images in a larger range toward the front of the screen insteadof the axisymmetrical range. In the modification of the firstembodiment, the sphere constituting the screen has the opening 8. Anembodiment, where the sphere constituting a screen does not have anopening and each optical clement of a projection optical system is noton the same optical axis, is explained as a third embodiment below.

The function of the full-surround spherical screen projection system Iof the first embodiment in accordance with the invention with thestructure shown above will be described below. When seeing the pictureson the spherical screen 2, a viewer P is almost at the central axis ofthe spherical screen 2. The projection light from the projector 3 iscast in a downward direction in the Drawing to be reflected upward tothe second reflecting mirror 5 by the first reflecting mirror 4. Thereflected light is reflected once again by the mirror of the secondreflecting mirror 5 and spread downward. The projection images are castto the viewer without interference on the entire circumferential surfaceof the spherical screen 2 except for the top and bottom of the sphere 7.

According to the full-surround spherical screen projection system 1, theviewer P can, from the interior of the spherical screen 2, observe theimages projected on the entire circumferential surface of the sphericalscreen except for the top and bottom of the sphere. Generally, it iswhen a light source is directly above that the shadow of the viewerbecomes the smallest. Utilizing that principle and setting theprojection optical system of the full-surround spherical screen over thehead of the viewer reduce the portion blocked from being projected on bythe viewer.

With the full-surround spherical screen projection system of theinvention, the pictures cannot, in principle, be projected to the topand bottom of the sphere. However, this point does not generally produceany inconvenience with the full-surround spherical screen projectionsystem of the invention, because people do not look directly aboveand/or below when observing scenery. When the full-surround sphericalscreen projection system of the invention is used to obtain images atthe bottom, a floor projection screen for back projection may beprepared separately.

When the recorded images are projected on the screen by thefull-surround spherical screen projection system of the invention,distortion is produced in the screen images. Accordingly, it isnecessary beforehand to distort the images to be cast so that the viewersees no distortion when the images are projected on the screen.

This will be explained in FIG. 3. An outer circle 20, an intermediatecircle 21 and an inner circle 22 in the rectangular image 19 for theprojection system are, as shown in FIG. 3(a), placed at non-equalintervals between the adjacent circles of the three circles. However,the circles are, as shown in FIG. 3(b), projected as an upper circle20′, an intermediate circle 21′ and a lower circle 22′ at equalintervals on the spherical screen 2. Points K, L and M in therectangular image are projected as K′, L′ and M′ on the spherical screen2. Therefore, the circles at equal intervals thrown on the sphericalscreen 2 of FIG. 3(b) are not placed at equal intervals on therectangular image 19 for the projection system in FIG. 3(a), at thestage of recording or making CG. That is, the images must be madebeforehand as distorted circles.

To form images with distortion beforehand in recording, an imagerecording apparatus 23 as shown as an embodiment in FIG. 4 is used. Therecording apparatus 23 includes a recording camera 24 and an ellipticalconvex mirror 25 placed above the recording camera 24. When recording asubject in the area of an angle α defined by a straight line k and astraight line m, a point K″ on the line k, a point M″ on the line m, andL″ on the line I are recorded as K, L, and M, respectively, of therectangular image distorted beforehand as shown in FIG. 3(a), throughthe elliptical convex mirror 25 by the recording camera 24.

When designing the suitable position of a focal point of the ellipticalconvex mirror 25, taking into consideration the second reflecting mirror5 of the full surround screen projection system 1, distortionless imageswill be thrown on the spherical screen 2. When recorded images ofsurrounding scenery obtained by the recording apparatus 23 are cast bythe projector, the viewer can observe the image scenery with virtualpresence, as if he were observing the surrounding scenery at the placewhere the images were recorded. As for CG images, considering thedistortion that will be produced in casting, recorded images can becreated by a computer.

In the first embodiment above, an opening 8 is formed at the top of thesphere. The projector 3 is placed opposed to the opening 8. However itis not necessary to have an opening at the top of the sphere. It ispossible that by providing a large spherical screen in a large room, aviewer can be completely inside of the spherical screen for viewing. Itis anticipated that the projection system will be made increasinglycompact in the future. If the projection system is compact enough, itcan be arranged inside of the spherical screen. The projector may beplaced away from, not at, the top of the sphere. This example will beexplained as a second embodiment.

FIG. 5 shows a second embodiment of a full-surround spherical screenprojection system 26 in accordance with the invention in which a largespherical screen 28 is provided in a large room 27 such as a theater. Inthe full-surround spherical screen projection system 26, a screen 28does not have the openings shown in the first embodiment, apart from anentrance for people and materials. The structure is made so that theviewer can be inside the spherical screen 28 for viewing. A projector 29is provided inside of the spherical screen 28. The projector 29, a firstreflecting mirror 30 and a second reflecting mirror 31 are on the sameoptical axis, as in the first embodiment. The first reflecting mirror 30is either a plane mirror or a convex mirror; the second reflectingmirror 31 is a circular concave mirror or a half mirror, whose functionsare the same as those in the first embodiment.

In the first and second embodiments, the projector 3/29 is arrangedfurther away from the second reflecting mirror 5/31 with reference tothe first reflecting mirror 4/30, because this prevents the projector3/29 from producing a shadow when the reflecting light is cast from thefirst reflecting mirror 4/30. However, if the projector 3/29 is small,even if the projector 3/29 is placed at a more inner position than thesecond reflecting mirror 5/31 with reference to the first reflectingmirror 4/30, a shadow produced by the projector 3/29 is small and withina range corresponding to the dead space above and does not result in alack of images. Accordingly, if the projector 3/29 is made small, theprojector 3/29 may be placed at a more inner position than the secondreflecting mirror 5/31 with reference to the first reflecting mirror4/30. In this case, the second reflecting mirror 5/31 does not have tobe a circular reflecting mirror or a half mirror as in the first andsecond embodiments, and can be a convex mirror such as a commerciallyavailable comer mirror.

FIG. 6 shows a full-surround spherical screen projection system 32 of athird embodiment in accordance with the invention. Although theprojector and the first and second reflecting mirrors arc on the sameoptical axis in the first and second embodiments and axisymmetric, theoptical positioning of those optical elements in the full-surroundspherical screen projection system 32 of the third embodiment isdifferent.

In the full-surround spherical screen projection system 32, a projector33 is placed away from the top of a spherical screen 34 at a slant. Afirst reflecting mirror 35 such as a plane mirror or a concave mirror isput at a slant under the top of a spherical screen 34. Above the firstreflecting mirror 35 is arranged at a slant a second reflecting mirror36 of a convex mirror. The first and second reflecting mirrors 35 and 36sequentially reflect the projected light from the projector 33, and theimages are projected onto the spherical screen 34.

By the full-surround spherical screen projection system 32 having theabove structures, the images is projected in a wide range W on thescreen in front of the projector 33 (left screen in FIG. 6), but in anarrow range N on the screen behind the projector (right screen in FIG.6). That is, the images are projected asymmetrically with respect to theaxis. Because the second reflecting mirror, which does not have holes oris not a half-mirror in the first and second embodiments, may be aconvex mirror such as a commercially available comer mirror, it can beoperated very easily.

The full-surround spherical screen projection system 32 does not allowthe viewer to look at the images on nearly the entire sphere with thesame upper and lower visual field angles by looking to the back orturning to the side as in the full-surround spherical screen projectionsystem 1/26 of the first and second embodiments, but allows the viewerto look at all the images in the visual field defined by the viewer'ssitting position. Accordingly, it is applicable to a flight simulatorwhere the images in the visual field can be changed for operationpractice while sitting at an operation seat.

As explained above, according to the full-surround spherical screenprojection systems, the spherical screen is formed on the inside of thesphere, a single-eye projector is provided that projects the imagestoward the inside of the sphere, a first reflecting mirror opposed tothe projector is provided inside the spherical screen, a secondreflecting mirror near the projector is provided, and the projectedimages from the projector are projected onto the spherical screen viathe first and second reflecting mirrors. In this way, the invention hasa simple and low-cost structure of the single-eye projector only, andcan project images with virtual presence on the entire spherical screenexcept for the top and bottom of the sphere, without a shadow of theviewer.

The invention may use a plane mirror or a concave mirror as the firstreflecting mirror. When a plane mirror is used, the visual field anglecan be widened in the upper and lower directions. If a concave minor isemployed, the distance to the projector can be shortened, which leads toa compact optical projection system. In addition, since the inventionallows the optical projection system to place the spherical mirror abovethe center of the sphere forming a spherical mirror, the viewer can seewell with increased leeway while standing.

Since the invention distorts original images beforehand at the stage ofmanufacturing the original images by recording or CG so that thedistortion can be cancelled when the original images are projected,there will be no distortion in the images projected on the sphericalscreen.

INDUSTRIAL APPLICABILITY

If the scenery of cities and towns or the look of stores and houses indesign stages are simulated by a computer, their images are formed andthe formed images are projected by a projector, the full-surroundspherical screen projection systems of the invention enableunderstanding of the surroundings and their impressions in all thedirections without constructing real cities and towns and building realhousing spaces. Therefore, the invention can be used as a valuableevaluation or supplemental means for the design of cities, towns,buildings, and housing spaces.

When images of the surroundings as seen from a cockpit of an airplaneare recorded or simulated by a computer and projected on a sphericalscreen by the full-surround spherical screen projection system of theinvention to use as a flight simulator, simulated operation practice canbe conducted in a situation close to real scenery shown in all thedirections.

When astronomical objects in continuous transition are transformer intoimages to be projected onto a spherical screen by the full-surroundspherical screen projection system, only one single-eye projector isneeded without the need to use a plurality of projectors as in the priorart, which provides a planetarium with economical facilities.

What is claimed is:
 1. A full-surround spherical screen projectionsystem comprising: a spherical screen formed inside of a sphere; aprojector for projecting light toward the inside of said sphere, saidprojector emitting a pre-distorted image of a subject, whichpre-distorted image is configured to be cast on said spherical screen; afirst reflecting mirror comprising either one of a plane mirror or aconcave mirror, placed away from the center of said sphere inside ofsaid sphere, for reflecting the light toward the outside of said sphere;and a second reflecting mirror constituting a convex mirror reflectingthe light from said first reflecting mirror to said spherical screen,said second reflecting mirror being disposed further away from thecenter of said sphere than is said first reflecting mirror, said convexmirror being configured to compensate for the distortions of thepre-distorted image, whereby an image of the subject is cast on thespherical screen without distortions.
 2. The full-surround sphericalscreen projection system of claim 1, wherein said sphere has an openingat a portion thereof, and said second reflecting mirror is placed inopposed to said opening within a radius from the center of said sphere.3. The full-surround spherical screen projection system of claim 2,wherein said projector and said first and second reflecting mirrors areplaced on the same optical axis, and said second reflecting mirror iseither a circular reflecting mirror with a central hole that passes thelight through from said projector or a half mirror.
 4. An imagerecording apparatus for the full-surround spherical screen projectionsystem of claim 3, comprising: an elliptical convex mirror according tothe curvature of said second reflecting mirror; and a recording camerafor recording a subject through said elliptical convex mirror.
 5. Thefull-surround spherical screen projection system of claim 2, whereinsaid projector and said second reflecting mirror are placed apart to theside along the inner wall of said sphere.
 6. An image recordingapparatus for the full-surround spherical screen projection system ofclaim 5, comprising: an elliptical convex mirror according to thecurvature of said second reflecting mirror; and a recording camera forrecording a subject through said elliptical convex mirror.
 7. An imagerecording apparatus for the full-surround spherical screen projectionsystem of claim 2, comprising: an elliptical convex mirror according tothe curvature of said second reflecting mirror; and a recording camerafor recording a subject through said elliptical convex mirror.
 8. Thefull-surround spherical screen projection system of claim 1, whereinsaid projector and said first and second reflecting mirrors are placedon the same optical axis, and said second reflecting mirror is either acircular reflecting mirror with central hole that passes the lightthrough from said projector or a half mirror.
 9. An image recordingapparatus for the full-surround spherical screen projection system ofclaim 8, comprising: an elliptical convex mirror according to thecurvature of said second reflecting mirror; and a recording camera forrecording a subject through said elliptical convex mirror.
 10. Thefull-surround spherical screen projection system of claim 1, whereinsaid projector and said second reflecting mirror are placed apart to theside along the inner wall of said sphere.
 11. An image recordingapparatus for the full-surround spherical screen projection system ofclaim 10, comprising: an elliptical convex mirror according to thecurvature of said second reflecting mirror; and a recording camera forrecording a subject through said elliptical convex mirror.
 12. An imagerecording apparatus for the full-surround spherical screen projectionsystem of claim 1, comprising; an elliptical convex mirror according tothe curvature of said second reflecting mirror; and a recording camerafor recording a subject through said elliptical convex mirror.
 13. Thesystem according to claim 1, wherein the second reflecting mirror isdisposed close to a periphery of the sphere.
 14. The system according toclaim 1, wherein said pre-distorted image is an image recorded throughthe convex mirror using an image recording apparatus including theconvex mirror.
 15. The system according to claim 1, wherein saidpre-distorted image is an image generated using a computer graphictechnique.
 16. An apparatus comprising: a full-surround sphericalscreen; a projector; and a means for projecting images substantiallywithout distortions onto said full-surround spherical screen from saidprojector, said means being located away from the center of saidfull-surround spherical screen.